Presently in communication systems, particularly cellular communication systems, it is necessary to change the frequency plan from time-to-time. This need arises from a variety of circumstances such as capacity needs during particular times of day or the redesign of a system through the placement of additional cell sites.
The current methods of changing a frequency plan require either that part of the system be shut down or results in substantial interference during the transition from the old to the new frequency plan. One present method of accomplishing an allocation of a new frequency plan consists of allocating the new frequencies and locking out the old frequencies once calls are completed. This results in calls handled on old frequencies interfering with calls being handled on new frequencies in the same or adjacent cells during the overlap time.
Another method of changing a frequency plan is performed in the GSM (Groupe Special Mobile currently known as Global System for Mobile communications). In GSM, timing is established for transitioning a mobile station from one channel to a new channel. This is possible in GSM because of the use of superframes which are numbered and allow more precise timing between the BTS (Base Transceiver Station) and the mobile station. At the designated frame number, the system hands-off the communication unit from an old frequency to a new frequency. This capability can be used to help minimize the transitional period while the system is going from the old to the new frequency plan.
However other cellular communication protocols do not provide for frame numbering (which provides the capability of synchronizing the transfer of mobiles from the old set of channels to the new set) and do not have the timing accuracy utilized in GSM. TDMA (Time Division Multiple Access) systems such as EIA/TIA IS-54 (Electronics Industry Association/Telecommunications Industry Association Interim Standard 54), Japan's PDC (Personal Digital Cellular) system, described in RCR 27 (Research and development Center for Radio standard 27), and various analog systems, such as the EIA/TIA standard 553, do not have such a timing equivalent. Therefore, it is necessary to develop a process by which frequency plans can be changed in a manner resulting in reduced impact on the system and system users.
It should be noted that the use of the term frequency plan herein is the currently accepted designation which describes the set of channels used for communication with the mobile stations. I will be understood by those of skill in the art that frequency plans will also relate to time slot allocations, as well as identifying signals such as SAT (Supervisory Audio Tone), DVCC (Digital Verification Channel Code), etc.